Radiation detector and imaging system

ABSTRACT

The invention relates to a radiation detector ( 100; 101; 102; 103; 104; 105; 106 ), having a scintillator ( 120 ) for generating electromagnetic radiation ( 202 ) in response to the action of incident radiation ( 200 ). The scintillator ( 120 ) has two opposing end faces ( 121; 122 ) and a lateral wall ( 123 ) between the end faces ( 121; 122 ). The radiation detector has, in addition, a conversion system ( 160 ) located on the lateral wall ( 123 ) of the scintillator ( 120 ), said system comprising a plurality of channels ( 165 ). Each channel ( 165 ) has a photocathode section ( 130; 131; 132 ) for generating electrons ( 204 ) in response to the action of electromagnetic radiation ( 202 ) that is generated by the scintillator ( 120 ), said electrons being multipliable by impact processes in the channels ( 165 ). A detection system ( 170 ) for detecting electrons ( 204 ) that have been multiplied in the channels ( 165 ) of the conversion system ( 160 ) is also provided. The invention also relates to an imaging system ( 110 ) comprising a radiation detector of this type ( 100; 101; 102; 103; 104; 105; 106 ).

The present invention relates to a radiation detector which can be usedto detect electromagnetic radiation, in particular X-ray or gammaradiation. The invention furthermore relates to an imaging system,comprising such a radiation detector.

Imaging systems appertaining to medical technology are becomingincreasingly important nowadays. Systems of this type are used togenerate two- or three-dimensional image data of organs and structuresof the human body, which can be used for example for diagnosing causesof illness, for carrying out operations and for preparing therapeuticmeasures. The image data can be generated on the basis of measurementsignals obtained with the aid of a radiation detector.

This is the case for example in X-ray and computed tomography systems(CT). In systems of this type, the body or a body section of a patientto be examined is radiographed by means of X-ray radiation generated bya radiation source. The non-absorbed, transmitted portion of radiationis detected by a detector.

A further example is image generation with the aid of radionuclides,such as is used in positron emission tomography systems (PET) and singlephoton emission computer tomography systems (SPECT). In this case, thepatient to be examined is injected with a radiopharmaceutical whichgenerates gamma quanta either directly (SPECT) or indirectly (PET)through emission of positrons. The gamma radiation is detected by acorresponding radiation detector.

Detectors which can be used for the energy-resolved detection or“counting” of radiation quanta can operate according to differentmeasurement principles. Radiation can be detected either directly, i.e.by direct conversion of the radiation energy into electrical energy, orindirectly. In the case of the last-mentioned variant, use is generallymade of a so-called scintillator, which is excited in response to theaction of radiation to be detected and reemits the excitation energy byemitting lower-energy electromagnetic radiation. Only the radiationemitted by the scintillator is converted into electrical measurementsignals in this case. Detectors of planar construction (so-called “flatdetectors”) which are used in the medical field and operate inaccordance with these measurement principles are described for examplein M. Spahn, “Flat detectors and their clinical applications”, EurRadiol (2005), 15: 1934-1947.

The conversion of the radiation emerging from a scintillator into anelectrical signal can be effected in various ways. Besides use of aphotomultiplier provided with a photocathode in the form of an evacuatedelectron tube, one concept that is common at the present time consistsin using a so-called silicon photomultiplier (“SiPM”). This involves amatrix arrangement of avalanche photodiodes (APD) embodied on a sharedsubstrate, electrons being generated in said photodiodes as a result ofincident photons, and said electrons being multiplied in anavalanche-like manner.

One disadvantage of silicon photomultipliers, however, is that only partof the total area available for irradiation can be utilized as sensitiveor “active” area. The reason for this is that between the active orradiation-sensitive regions there are also insensitive regions, in whichresistors and signal lines or wiring structures are arranged. A siliconphotomultiplier therefore has a relatively small ratio of active area to(irradiated) total area, said ratio also being designated as “fillingfactor”. Further disadvantages include noise that occurs duringoperation, and a relatively high dark rate or dark count, that is to saythat signal generation takes place even without irradiation.

A detector comprising a scintillator and a silicon photomultiplier isusually embodied in such a way that the silicon photomultiplier isopposite an end face or rear side of the scintillator. An opposite endface or front side of the scintillator faces the radiation to bedetected. As a result, the silicon photomultiplier can detect only thatportion of the radiation converted in the scintillator which emerges atthe rear side thereof. Proceeding from the respective excitation orinteraction location in the scintillator, however, the scintillationradiation is emitted not only in the direction of the rear side, butalso in other directions. Furthermore, the radiation is subject to lossprocesses such as reflection, absorption and scattering. Particularly inthe case of scintillators having a high aspect ratio, i.e. a high ratioof height to width, as may be the case for example in a PET system, thelosses are therefore relatively high. In the case of an aspect ratio ofgreater than 7:1, the radiation emerging from a scintillator may make upa proportion of merely 40-60% of the total radiation generated. Althougha higher intensity of the incident radiation can be provided in order tocompensate for the losses, as a result a patient is also exposed to anincreased radiation dose.

It is furthermore disadvantageous that an interaction location ofincident radiation in a scintillator cannot be detected or can bedetected only with very great difficulty on the basis of the radiationemerging at the rear side of the scintillator. Moreover, it is notpossible to obtain information about the height or depth of aninteraction in the scintillator. Such disadvantages therefore restrictthe resolution of an imaging system provided with such a detectorconstruction.

For image intensification and for electron multiplication, it isfurthermore known to use so-called microchannel plates (MCP) having amultiplicity of channels. During operation, an electrical voltagepresent along the channels is generated, whereby entering electrons canbe accelerated within the channels and multiplied by impacts with thechannel walls. Use of a microchannel plate in connection with an imageintensifier is described in US 2009/0256063 A1, for example.

The object of the present invention is to specify a solution forimproved radiation detection in the medical field.

This object is achieved by means of a radiation detector as claimed inclaim 1 and by means of an imaging system as claimed in claim 15.Further advantageous embodiments of the invention are specified in thedependent claims.

The invention proposes a radiation detector comprising a scintillatorfor generating electromagnetic radiation in response to the action ofincident radiation. The scintillator has two mutually opposite end facesand a lateral wall between the end faces. The radiation detectionfurthermore comprises a conversion device arranged on the lateral wallof the scintillator and having a plurality of channels. In this case,each channel has a photocathode section for generating electrons inresponse to the action of the electromagnetic radiation generated by thescintillator, said electrons being multipliable as a result of impactprocesses in the channels. A detection device for detecting electronsmultiplied in the channels of the conversion device is furthermoreprovided.

During the operation of the radiation detector, with one of the endfaces the scintillator can face the radiation to be detected (inparticular X-ray or gamma radiation). The electromagnetic radiation (forexample visible or ultraviolet light) generated by the incidentradiation in the scintillator and passing to the lateral wall thereofcan be converted into electrons directly by the conversion devicearranged at this location, which conversion device can be regarded as acombination of a microchannel plate and a photocathode. In this case,the radiation emitted by the scintillator is firstly taken up orabsorbed by the photocathode sections of the channels, as a result ofwhich electrons are liberated, which can be multiplied further in thechannels (“electron path”). The conversion device can thus convert thescintillation radiation rapidly and directly into a multiplicity ofelectrons which can be detected by the detection device. The arrangementof the conversion device on the lateral wall of the scintillator affordsthe possibility of utilizing a large part of the radiation converted inthe scintillator for generating electrons. This holds true particularlyin the case of one possible configuration of the scintillator having ahigh aspect ratio, as a result of which the lateral wall can also have arelatively large surface area in comparison with the end faces. Onaccount of these properties, the radiation detector can be distinguishedby a high temporal resolution and high efficiency.

It is furthermore advantageous that the radiation detector can have(significantly) less noise and a lower dark rate compared with theconventional detector comprising a silicon photomultiplier. This can beattributed to the fact that without radiation of the scintillator noelectrons are generated by the photocathode sections and, consequently,(substantially) no electron multiplication takes place in the channelsof the conversion device. Moreover, the channels of the conversiondevice can be arranged at a small distance from one another or alongsideone another on the lateral wall of the scintillator, as a result ofwhich a high filling factor (ratio of active area to irradiated totalarea) can be present, which can be (significantly) higher than in thecase of a conventional silicon photomultiplier. This likewise fosters ahigh efficiency of the radiation detector.

In one preferred embodiment, the detection device has an electrode fortrapping electrons, said electrode being arranged at one end of thechannels. Furthermore, a counterelectrode is arranged at an opposite endof the channels in order to bring about a movement of electrons to theelectrode of the detection device. As a result, the electrons generatedby the photocathode sections can be reliably moved or accelerated in thedirection of the electrode. Moreover, the electrons can collide with thechannel walls during the movement, as a result of which a multiplicityof (further) electrons can be liberated.

In a further preferred embodiment, the lateral wall of the scintillatoris embodied in a planar fashion. Furthermore, the conversion device isembodied in the form of a plate-shaped structure on the lateral wall ofthe scintillator. This affords the possibility of a space-savingconfiguration of the conversion device, which can furthermore berealized in a relatively simple manner. In particular, the conversiondevice (or part thereof) can arise from a structured substrate which canbe arranged on or connected to the planar lateral wall of thescintillator.

In one preferred embodiment constituting an alternative to this, thelateral wall of the scintillator has depressions through which thechannels of the conversion device are formed. Such a configuration canlikewise be distinguished by a space-saving and simple construction. Thechannels embodied in the form of depressions can be closed in a suitablemanner on the lateral wall of the scintillator, for example with the aidof a substrate or carrier element arranged on the lateral wall.

In a further preferred embodiment, which can be realized in a simple andcost-effective manner, the photocathode sections of the channels of theconversion device are embodied in the form of a continuous photocathode.In this case, the photocathode is preferably arranged on a carrierelement.

In a further preferred embodiment, the lateral wall of the scintillatoris provided with a layer transmissive to the electromagnetic radiationgenerated by the scintillator. Such a layer, which can serve as anentrance window for the channels of the conversion device, can minimizeor suppress reflection of the radiation converted by the scintillator atthe lateral wall. In this way, a high efficiency of the radiationdetector can be fostered further.

This likewise applies to one further preferred embodiment, according towhich the channels of the conversion device have a wall coating designedto liberate a plurality of electrons per impact process of an electron.In particular, a material having high secondary electron emission isused for the wall coating.

The channels of the conversion device preferably run parallel to alongitudinal axis of the scintillator, said longitudinal axis extendingbetween the end faces. In this configuration, the detection device canbe arranged in the region of an end face of the scintillator, as aresult of which a relatively compact detector construction is possible.

In a further preferred embodiment, the scintillator is embodied in aparallelepipedal fashion and has four lateral walls between the endfaces. A conversion device having a plurality of channels is arranged oneach of the four lateral walls.

As a result, a significant part of the electromagnetic radiationgenerated in the scintillator can be converted into electrons, which isfurthermore advantageous for a high efficiency of the radiationdetector.

In a further preferred embodiment, the detection device is designed forseparately detecting electrons generated and multiplied in channels ofdifferent conversion devices or in channels of different subsections ofa conversion device. This affords the possibility of accuratelydetecting the lateral location of an interaction of a radiation quantuminteracting with the scintillator. In this case, the detection devicecan have different electrode regions or segments for separately trappingelectrons.

In a further preferred embodiment, the radiation detector is designed tobring about a movement of electrons in channels of different conversiondevices or in channels of different subsections of a conversion devicein different directions. This can be realized with correspondingelectrode arrangements. On the basis of this or as a result of(separate) detection of the electrons accelerated in differentdirections, the possibility is afforded of accurately detecting theheight or depth of an interaction in the scintillator.

In a further preferred embodiment, the radiation detector isadditionally designed to convert part of the electromagnetic radiationgenerated in the scintillator and emerging at an end face into electronsand to detect the electrons. For this purpose, the radiation detectorcan comprise, for example, a further photocathode section for generatingelectrons in response to the action of the electromagnetic radiationgenerated by the scintillator in the region of the end face of thescintillator. The electrons emitted here can be multiplied with the aidof a (conventional) microchannel plate, and subsequently be detected bythe detection device. Such a configuration can likewise be advantageousfor a high efficiency of the radiation detector.

In a further preferred embodiment, the radiation detector comprises twoscintillators arranged alongside one another. In this case, provision ismade of conversion devices arranged in an interspace between thescintillators and on opposite lateral walls of the scintillators andassigned to the scintillators and having a plurality of channels. Theradiation detector further comprises a detection device for detectingelectrons, said detection device being assigned to the conversiondevices. In the case of such a modular construction of the radiationdetector, which can also be realized with more than two scintillatorsarranged alongside one another, it is possible to make use of the factthat the conversion devices can be configured in a space-saving manner,as a result of which the interspace between the scintillators can alsobe kept as small as possible. A high filling factor and hence efficiencycan be obtained as a result.

The invention furthermore proposes an imaging system which comprises aradiation detector in accordance with one of the embodiments describedabove, and in which, therefore, the advantages described above canlikewise be manifested. Such an imaging system can be, for example, anX-ray or computed tomography system or else a positron emissiontomography or single photon emission computed tomography system. Withregard to such imaging systems, provision can be made for theabove-described detector construction or one of the above-describedembodiments to constitute in each case an individual detector element ora “pixel” of an associated detector, and for a multiplicity of suchdetector elements or “pixels” to be arranged alongside one another inparticular in a planar fashion and/or in a circular or partly circularfashion.

The above-described properties, features and advantages of thisinvention and the way in which they are achieved will become clearer andmore clearly understood in association with the following description ofexemplary embodiments which are explained in greater detail inassociation with the drawings, in which:

FIG. 1 shows a schematic illustration of an X-ray system;

FIG. 2 shows a schematic perspective illustration of component parts ofa detector element, comprising a scintillator and a conversion devicefor converting scintillation radiation into electrons, said conversiondevice being arranged on a lateral wall of the scintillator;

FIG. 3 shows a schematic plan view illustration of an excerpt from aplate-shaped conversion device arranged on a scintillator;

FIG. 4 shows a schematic perspective illustration of the conversiondevice from FIG. 3;

FIG. 5 shows a schematic plan view illustration of an excerpt from afurther plate-shaped conversion device arranged on a scintillator;

FIG. 6 shows a schematic perspective illustration of a detector elementcomprising a plurality of conversion devices, which is designed todetect segment by segment electrons generated in the differentconversion devices;

FIG. 7 shows a schematic perspective illustration of a further detectorelement comprising a plurality of conversion devices, which is designedto move electrons generated in the different conversion devices indifferent directions;

FIG. 8 shows a schematic plan view illustration of an excerpt from twoscintillators arranged alongside one another and conversion deviceswhich are assigned to the scintillators and which are arranged in aninterspace between the scintillators;

FIG. 9 shows a schematic perspective illustration of a further detectorelement constructed in a manner corresponding to FIG. 8;

FIGS. 10 to 13 show a schematic illustration of a production of theconstruction comprising two scintillators and conversion devicesassigned to the scintillators, as shown in FIG. 8;

FIG. 14 shows a schematic plan view illustration of an excerpt from twoscintillators arranged alongside one another and conversion deviceswhich are assigned to the scintillators and the channels of which areembodied in the form of depressions in the scintillators;

FIG. 15 shows a schematic perspective illustration of the twoscintillators from FIG. 14;

FIG. 16 shows a schematic perspective illustration of a further detectorelement constructed in a manner corresponding to FIG. 15; and

FIG. 17 shows a schematic lateral illustration of a further detectorelement, which is designed additionally to convert a portion ofscintillation radiation that emerges at an end face of a scintillatorinto electrons.

Embodiments of a detector or detector element which can be used todetect electromagnetic radiation, in particular high-energy radiationsuch as X-ray or gamma radiation, are described with reference to thefollowing figures. In order to produce the embodiments described, methodprocesses known from the field of semiconductor and detector technologycan be carried out and customary materials can be used, and so they willbe discussed only in part.

The detector concept described here is provided for use in associationwith imaging systems appertaining to medical technology. In systems ofthis type, two- or three-dimensional image data of organs and structuresof the human body are generated on the basis of measurement signalsobtained with the aid of a corresponding radiation detector.

For exemplary elucidation, FIG. 1 illustrates an X-ray system 110 whichcan be used for diagnostic and interventional imaging. The X-ray system110 comprises a radiation source 111 for emitting X-ray radiation(“X-ray emitter”) and an associated detector 100 of planar construction(“flat detector”) for detecting the radiation. Radiation source 111 anddetector 100 are arranged opposite one another at the ends of a C-shapedholding device 112. On account of this configuration, this arrangementis also designated as “C-arc” or “C-arm”.

A patient to be examined is situated on a patient supporting couch 117and in this case is arranged between radiation source 111 and detector100. During the operation of the X-ray system 110, the body or a bodysection of the patient is radiographed with the X-ray radiationgenerated by the radiation source 111, and the non-absorbed, transmittedportion of radiation is detected by means of the detector 100.

The holding device 112 is furthermore fixed to a robot 113 provided witha plurality of axes and/or articulations, with the aid of which robotthe radiation source 111 and the detector 100 can be brought to adesired position in relation to the patient. For controlling the X-raysystem 110 and for processing and/or evaluating measurement signals ofthe detector 100, in particular for generating the desired image data,the X-ray system 110 furthermore comprises a control and/or evaluationdevice 114. The latter is connected to a corresponding display device ora display, as is indicated in FIG. 1.

Alongside the X-ray system 110 from FIG. 1, the detector conceptdescribed below can also be used in association with other imagingsystems (not illustrated). By way of example, systems comprising agantry, such as a computed tomography system (CT), for example, areappropriate. Such a system can comprise an annular orcircular-cylindrical detector and a rotatable X-ray source. Furtherexemplary applications with a gantry include positron emissiontomography systems (PET) and single photon emission computed tomographysystems (SPECT). In this case, the patient to be examined is injectedwith a radiopharmaceutical which generates gamma quanta either directly(SPECT) or indirectly (PET) through emission of positrons. Said quantacan be detected likewise by an annular or circular-cylindrical detector.

FIG. 2 shows a schematic perspective illustration of a basicconstruction of a detector element 101 which can be used for detectingincident high-energy radiation. The embodiments of detector elementsdescribed further below with reference to the other figures areconstructed on the basis of the detector principle shown here, and sothe aspects described below can also apply to these embodiments.Furthermore, it is pointed out that a radiation detector of an imagingsystem, for example the detector 100 of the system 110 from FIG. 1, cancomprise a multiplicity of detector elements constructed in this way,wherein said detector elements can be arranged alongside one another inthe form of “pixels” in a matrix-like manner. In this case, inparticular, planar, but also annular or partly annular arrangements canbe present. The image data respectively desired can be generated on thebasis of the measurement signals generated by the individual pixels ordetector elements of a detector.

As is illustrated in FIG. 2, the detector element 101 has a scintillator120, which serves to convert the high-energy radiation to be detectedinto a low(er)-energy radiation. The scintillator 120 is embodied in aparallelepipedal fashion and has two mutually opposite end faces 121,122 and four lateral walls 123 between the two end faces 121, 122, saidlateral walls adjoining one another at a right angle. The end face 122directed toward the top in FIG. 2 is also designated hereinafter as“front side” and the end face 121 directed toward the bottom as “rearside” of the scintillator 120. Front and rear sides 122, 121 areconnected to one another via the lateral walls 123 at the periphery oredge.

As is furthermore indicated in FIG. 2, the scintillator 120 has a highaspect ratio, i.e. a high ratio of height (distance between the endfaces 121, 122) to width (lateral dimension or distance between twomutually opposite lateral walls 123), which is greater or significantlygreater than one. In this way, it is possible to obtain a highabsorption of the high-energy radiation to be detected, which isindicated on the basis of a radiation quantum 200 in FIG. 2, in thescintillator 120. In this connection it is pointed out that thecomponents illustrated in FIG. 2, but also in the other figures, andtheir dimensions may be illustrated in a manner not true to scale. Byway of example, it is possible for the scintillator 120 to have a largerheight or a larger aspect ratio.

During the operation of the detector element 101, the front side 122 ofthe scintillator 120 faces the radiation to be detected, such that theradiation can be incident or coupled into the scintillator 120 via thefront side 122. A radiation quantum 200 (in particular X-ray quantum orgamma quantum) of the incident radiation can bring about an excitationlocally upon passing through the scintillator 120. The excitation energydeposited or absorbed during this process is reemitted by thescintillator 120 in the form of lower-energy radiation quanta or photons202. In this case, the number of emitted photons 202 may be proportionalto the original energy of the radiation quantum 200 that interacts withthe scintillator material. The scintillation mechanism which takes placein this case will not be discussed in more specific detail. Thescintillation radiation generated by the scintillator 120 may be visibleor ultraviolet light, in particular.

Alongside radiation emission in the direction of the end faces 121, 122of the scintillator 120, a large part of the scintillation radiation orphotons 202 generated in the scintillator 120 is emitted in thedirection of the lateral walls 123. This is the case, in particular, ifthe scintillator 120, as in the present case, has a high aspect ratio,and, consequently, the lateral walls 123 have a relatively large surfacearea in comparison with the end faces 121, 122 of the scintillator 120.The detector element 101, as illustrated in FIG. 2, is designed toutilize that portion of the scintillation radiation which passes to alateral wall 123 for the purpose of detecting radiation. Theconstruction shown here and described below can be provided, inparticular, on all of the four lateral walls 123, as a result of which ahigh detection efficiency or a high efficiency can be achieved.

For detecting the scintillation radiation, the detector element 101comprises a conversion device 160 arranged on the relevant lateral wall123. With the aid of the conversion device 160, photons 202 emitted inthe direction of the lateral wall 123 and emerging from the scintillator120 at the lateral wall 123 can be converted into electrons 204, and theelectrons 204 can be multiplied further. Preferably, the conversiondevice 160 has substantially the same external dimensions as the lateralwall 123, such that the lateral wall 123 can be substantially completely“covered” by the conversion device 160.

The conversion device 160 comprises a channel structure 161, 162, 163having a plurality of microscopically fine channels 165, which can alsobe designated as “microchannel”, “cell” or “microcell”. Variousconfigurations are possible for the conversion device 160 or the channelstructure 161, 162, 163 thereof. By way of example, a conversion device160 embodied in the form of a plate-shaped structure can be involved, inwhich the associated channel structure 161, 162 can comprise astructured substrate arranged on the lateral wall 123, as is describedin even greater detail further below in association with FIGS. 3 and 5.In an alternative configuration, the conversion device 160 can comprisea channel structure 163 in which the channels 165 are formed byindentations or depressions embodied in the lateral wall 123 of thescintillator 120, which will be described in even greater detail inparticular with reference to FIG. 14.

The channels 165, which, in a departure from the spaced-apartillustration in FIG. 2, are arranged in a plane alongside one another inthe region of the lateral wall 123 of the scintillator 120 and extendalong the lateral wall 123 or along a plane predefined by the lateralwall 123, preferably run—as indicated in FIG. 2—parallel to alongitudinal axis of the scintillator 120, said longitudinal axisextending between the end faces 121, 122. Each channel 165 of a channelarrangement 161, 162, 163 is furthermore provided with an internalphotocathode section, illustrated on the basis of a continuousphotocathode 130 in FIG. 2, such that photons 202 emerging at thelateral wall 123 can be converted into electrons 204 (photoelectrons)using the photoelectric effect in the channels 165. An electron 204 canbe liberated for each photon 202 which impinges on the photocathode 130or on a photocathode section and is absorbed here. In this case, in adeparture from the spaced-apart illustration in FIG. 2, the photocathode130 is situated in the region of or within the channels 165.Furthermore, it is pointed out that instead of the provision of thecontinuous photocathode 130 illustrated in FIG. 2, a configurationcomprising separate internal photocathode sections is also possible,which sections can be arranged separately from one another on or in eachchannel 165.

The electrons 204 emitted by the photocathode 130 or the photocathodesections can furthermore be multiplied by impact processes in thechannels 165 of the respective channel structure 161, 162, 163, and cansubsequently be detected. For this purpose, the detector element 101comprises an electrode arrangement comprising an electrode 150 and acounterelectrode 140 corresponding thereto, which, in a departure fromthe spaced-apart illustration in FIG. 2, are arranged at opposite endsof the conversion device 160 or the channel structure 161, 162, 163thereof. An electrical voltage (acceleration voltage) is applied to thetwo electrodes 140, 150, as a result of which an electric field presentalong the channels 165 is generated, which can be used to bring about amovement of the electrons 204 reliably in the direction of the electrode150. In this case, the electrode 140 constitutes a cathode, and theother electrode 150 constitutes an anode. For applying the voltage,which can be in the high-voltage range, in particular, the detectorelement 101 comprises a suitable connection structure (not illustrated).

The electrons 204 (primary electrons) emitted by the photocathode 130 orthe photocathode sections in the channels 165 can impact the (inner)walls of the associated channels 165 multiply during the movement oracceleration in the direction of the electrode 150 brought about by theelectric field, and upon each impact can eject or liberate furtherelectrons 204 (secondary electrons), which for their part can likewisebe accelerated within the channels 165 and liberate further electrons204 as a result of impacts with the channel walls. This processcontinues over the length of the channels 165 and is thereforeassociated with an avalanche- or cascade-like increase in electrons 204.For such functioning, the channels 165 have small lateral dimensions,for example in the micrometers range.

The electrons 204 multiplied in accordance with this process in thechannels 165 can pass to the electrode 150, which is simultaneously usedas a trapping or readout electrode (“readout pad”) for trapping orcollecting the (multiplied) electrons 204. The electrode 150, asindicated in FIG. 2, is part of a detection device 170 provided fordetecting electrons 204, which detection device can additionallycomprise a carrier element or a substrate 171, on which the electrode150 is arranged. The detection device 170 can be designed to generate,on the basis of the electrons 204 trapped by the electrode 150, acorresponding electrical output signal (for example voltage drop acrossa resistor). Such an output signal is dependent on the number or totalcharge of the collected electrons 204, and thus on the excitation energyoriginally deposited in the scintillator 120.

The detection device 170, as indicated in FIG. 2 is preferably arrangedin the region of the rear side 121 of the scintillator 120, as a resultof which a compact detector construction is possible. In this case, in adeparture from the illustration in FIG. 2, the carrier substrate 171 canalso extend below the scintillator 120, such that the carrier substrate171 can furthermore be utilized for bearing or supporting thescintillator 120 (cf. the exemplary embodiment in FIG. 9).

The arrangement of the conversion device 160 on the lateral wall 123 ofthe scintillator 120 affords the possibility of obtaining fast access toa large number of scintillation photons 202 by an extremely short route.In this case, the first “contact” of a photon 202 with the lateral wall123 or a photocathode section 130 arranged in the region of the lateralwall 123 can lead to the generation of an electron 204 which can bemultiplied further directly in the conversion device 160 or in a channel165 thereof. In one preferred configuration comprising conversiondevices 160 on all four lateral walls 123 (cf. the exemplary embodimentin FIG. 6), what can furthermore be achieved is that the radiation is(largely) prevented from being “reflected back and forth” in thescintillator 120, this being associated with corresponding lossprocesses, and a significant part of the radiation is thereforeconverted into electrons 204. In this way, the detector element 101 (anda comparably constructed detector element) can have a high efficiencyand a high temporal resolution. These advantages correspondingly alsohold true for a detector constructed from a plurality of such detectorelements, and thus for an associated imaging system. This affords thepossibility, in particular, of exposing a patient to be examined only toa low radiation dose.

The use of the channel structure 161, 162, 163 used for electronmultiplication furthermore makes it possible for the detector element101 (and a comparably constructed detector element) to have a low noiseproportion and a low dark rate. This is owing to the fact that theproduction of electron avalanches in the channels 165 and thus thegeneration of a corresponding signal in the detection device 170 takeplace (substantially) only if the scintillator 120 emits radiation andthe photocathode 130 generates photoelectrons 204 in response to theaction of the scintillation radiation. Furthermore, the channels 165 canbe at relatively small distances from one another, as a result of whicha high filling factor (ratio of active area to irradiated total area)can be present, which is likewise advantageous for the detectionefficiency.

The above-described functioning of the detector element 101 requires thepresence of an evacuated atmosphere or a vacuum (at least) in thatregion in which free electrons 204 are present, i.e. starting fromgeneration with the aid of the photocathode sections 130 through todetection with the aid of the detection device 170. For this purpose,provision can be made, for example, for each channel 165 of theconversion device 160 to be individually closed or sealed, and thereforeto be under vacuum. At the opposite ends of the channels 165, sealingcan be realized in particular with the aid of the two electrodes 140,150. Alternatively, “global” sealing of all channels 165 of theconversion device 160 together can also be provided. For this purpose,the detector element 101 can have, for example, a corresponding housing(cf. the exemplary embodiment in FIG. 9 with the housing 190).

The conversion device 160 arranged on the lateral wall 123 of thescintillator 120, which conversion device can be regarded as acombination of a planar or two-dimensional microchannel plate havingchannels 165 arranged “on a line” or in a plane and a photocathode 130,can, as has already been indicated above, be constructed in variousways.

One possible embodiment, illustrated in the schematic plan viewillustration in FIG. 3, is a plate-shaped conversion device 160 having achannel structure 161 formed from a structured substrate. In the case ofsuch a configuration, the lateral wall 123 of the scintillator 120 onwhich the conversion device 160 or the channel structure 161 thereof isarranged is furthermore embodied in a planar fashion. Only an individualchannel 165 of the channel structure 161 is illustrated in FIG. 3.However, the construction shown here applies to all channels 165 of thechannel structure 161, and is thus provided multiply alongside oneanother on the lateral wall 123 of the scintillator 120 (see FIG. 4).

As is illustrated in FIG. 3, the channel 165 has a rectangular geometryin plan view. The channel 165, the longitudinal axis of which runsperpendicularly to the plane of the drawing in FIG. 3, comprises, on twomutually opposite sides, in each case a cell or channel wall 166 presentin the form of a web. The channel walls 166, which can arise as a resultof structuring or production of trenches in a substrate 168 (see FIG.10), are connected at one end to the lateral wall 123 of thescintillator 120 or to a layer 180 optionally provided on the lateralwall 123.

The layer 180 constitutes an optical input or entrance window for thechannel 165, via which window scintillation photons 202 emitted in thedirection of the lateral wall 123 of the scintillator 120 can be coupledinto the channel 165, i.e. into an (evacuated) interior enclosed by thechannel 165. For this purpose, the layer 180 comprises a correspondingmaterial which is transmissive to the scintillation radiation generatedby the scintillator 120. The layer 180 can furthermore serve as anantireflection layer in order to minimize or suppress reflection of thescintillation radiation at the lateral wall 123 and, consequently,foster the detection efficiency further. The lateral wall 123 of thescintillator 120 can be substantially completely covered by the layer180, which can thus serve as entrance window and antireflection layerfor all channels 165 of the associated channel structure 161.Furthermore, the layer 180 can provide, if appropriate, for vacuum-tightclosure of the channels 165 in the region of the lateral wall 123 of thescintillator 120.

At an opposite end with respect thereto, the channel walls 166 of thechannel 165 shown in FIG. 3 are connected to a section 186 which canextend along all channels 165 of the channel structure 161. The section186 can be embodied, in particular, in the form of a separate substrateor carrier element, which can be connected to the channels walls 166 orthe associated structured initial substrate 168 from which the channelwalls 166 can arise. Vacuum-tight closure of the channels 165 canlikewise be effected by means of the section 186.

As is furthermore illustrated in FIG. 3, a section 131 of a photocathode130 is arranged on that side of the carrier section 186 which faces theenclosed interior of the channel 165. This involves a reflectivelyoperating, so-called reflection photocathode, which emits photoelectrons204 from that side on which the radiation coming from the scintillator120 also impinges. With regard to such reflective functioning, thephotocathode section 131 can be embodied in a solid fashion and with arelatively large thickness or layer thickness. This leads to a highreliability and efficiency in the conversion of the radiation emitted bythe scintillator 120 into photoelectrons 204.

A configuration in the form of separate photocathode sections 131assigned only to individual channels 165 on the section 186 is indicatedin FIG. 3. Preferably, however, all photocathode sections 131 of thechannels 165 are present in the form of a continuous (reflection)photocathode 130 arranged on the section 186 (cf. the exemplaryembodiment in FIG. 8), as a result of which simple and cost-effectiveproduction is made possible. In this case, the channel walls 166 of thechannels 165 can be connected to the carrier section 186 via thephotocathode 130.

FIG. 3 furthermore illustrates that the channel 165, at the interiorenclosed by the channel 165, is preferably provided with an additionalwall coating 181. The wall coating 181, which can be arranged both onthe web-shaped channel walls 166 and on the layer 180, serves to enablea multiplicity of electrons 204 to be liberated per impact process of anelectron 204, as a result of which the detection efficiency can befostered further. For this purpose, the wall coating 181 comprises, inparticular, a material having high secondary electron emission.

FIG. 3 furthermore illustrates the process of the generation andmultiplication of electrons 204 taking place in the illustrated channel165 of the channel structure 161. The scintillation photons 202 emittedby the scintillator 120 to the lateral wall 123 can penetrate throughthe layer 180 and the region of the wall coating 181 arranged thereon,enter into the interior of the channel 165, pass further to thereflective photocathode section 131 and be absorbed by the latter. Onthe basis of this, the photocathode section 131 can emit electrons 204.In this case, as is shown in the schematic perspective illustration inFIG. 4, the electrons 204 can be accelerated in the direction of theelectrode 150 with the aid of the two electrodes 140, 150. FIG. 4illustrates a view proceeding from the scintillator 120, wherein thescintillator 120 and the layer 180 are omitted. The small lateraldimensions of the channel 165 have the effect that the electrons 204 canimpact the wall or the wall coating 181 provided here multiply duringthis movement. Upon each impact, further electrons 204 can be releasedor ejected, which for their part can likewise be accelerated within thechannel 165 and liberate further electrons 204 as a result of impactswith the wall coating 181. The electrons 204 multiplied in this way aretrapped at the end of the channel 165 by the electrode 150 arranged atthis location.

FIG. 5 shows a schematic plan view illustration of a further embodimentof a plate-shaped conversion device 160 having a channel structure 162,which can be embodied in a manner similar to the channel structure 161described above, and likewise from a structured substrate. In thisconfiguration, too, the lateral wall 123 of the scintillator 120 onwhich the conversion device 160 or the channel structure 162 thereof isarranged is embodied in a planar fashion. Only an individual channel 165of the channel structure 162 is illustrated in FIG. 5. However, thisconstruction applies to all channels 165 of the channel structure 162,and is therefore provided multiply alongside one another on the lateralwall 123 of the scintillator 120.

As is illustrated in FIG. 5, the channel 165 once again has arectangular geometry in plan view. The channel 165, the longitudinalaxis of which runs perpendicularly to the plane of the drawing in FIG.5, comprises two mutually opposite channel walls 166. The channel walls166 are connected to one another at one end by means of a furtherchannel wall 167. With regard to the entire channel structure 162, thechannel wall 167 can extend along all channels 165, and, therefore, allchannel walls 166 of the individual channels 165 in accordance with theconstruction shown in FIG. 5 can be connected to the channel wall 167.In this case, there is the possibility of producing the arrangementcomprising the channel walls 166, 167 by producing trenches in asubstrate, with the removal of substrate regions between the channelwalls 166, 167.

At an opposite end relative to the channel wall 167, the channel walls166 are connected to the lateral wall 123 of the scintillator 122 or toa layer 180 once again optionally provided on the lateral wall 123. Thelayer 180 can again serve as an entrance window for the channel 165 orthe channels 165 of the channel structure 162, and as an antireflectionlayer, and, if appropriate, provide for vacuum-tight closure of thechannels 165 in the region of the lateral wall 123. For further detailsconcerning the layer 180, reference is made to the above explanationsconcerning FIG. 3.

As is furthermore illustrated in FIG. 5, a section 132 of a photocathode130 is arranged on that side of the layer 180 which faces the enclosedinterior of the channel 165. This involves a semitransparentphotocathode or transmission photocathode which operates transmissively.In this case, the photocathode section 132 is irradiated at the sidefacing the scintillator 120, and electrons 204 are emitted at theopposite side of the photocathode section 132 relative thereto into theinterior enclosed by the channel 165.

A configuration in the form of separate photocathode sections 132assigned only to individual channels 165 on the layer 180 is indicatedin FIG. 5 as well. Alternatively, it is possible for all photocathodesections 132 of the channels 165 to be present in the form of acontinuous (semitransparent) photocathode 130 arranged on the layer 180,as a result of which simple and cost-effective production is madepossible. In this case, the channel walls 166 of the channels 165 can beconnected to the layer 180 via the photocathode 130.

As is furthermore shown in FIG. 5, in the case of the channel structure162, too, the provision of an additional wall coating 181 in theinterior enclosed by the channel 165 can be considered, which additionalwall coating can be arranged both on the channel walls 166 and on thechannel wall 167. It once again serves to enable a multiplicity ofelectrons 204 to be liberated per impact process of an electron 204.

FIG. 5 furthermore illustrates the process of the generation andmultiplication of electrons 204 taking place in the illustrated channel165 of the channel structure 162. The scintillation photons 202 emittedby the scintillator 120 to the lateral wall 123 can penetrate throughthe layer 180, and can be absorbed by the photocathode section 132arranged here. On the basis of this, the photocathode section 132 canemit electrons 204 into the interior of the channel 165, which areaccelerated in the direction of the electrode 150 with the aid of theelectrodes 140, 150 (see FIG. 1), which are once again arranged at theends of the channel structure 162. On account of the small lateraldimensions of the channel 165, the electrons 204 can impact the wall, orthe wall coating 181 provided here, multiply during this movement. Uponeach impact, further electrons 204 can be liberated, which for theirpart are likewise accelerated within the channel 165 and contribute tothe electron multiplication as a result of impacts. The electrons 204multiplied in this way are trapped at the end of the channel 165 by theelectrode 150 arranged at this location.

Materials known from semiconductor and detector technology can be usedfor the detector components of the detector elements described here (andpossibly modifications thereof). The use of an inorganic material or ofa crystal is considered for the scintillator 120. Preferably, thisinvolves a “fast” scintillator 120, in which the scintillationmechanism, i.e. the conversion of the incident high-energy radiationinto the lower-energy scintillation radiation, takes place in a shorttime duration. One material considered for this purpose is CsF or LSO,for example. With regard to a possible size of the scintillator 120,consideration is given, for example, to lateral dimensions or a width inthe range of a few 100 μm to a few mm, and a height in the range of afew mm to a few 10 mm. In this case, the scintillator 120 has an aspectratio of (significantly) greater than one, which can be greater than7:1, for example, with regard to PET applications.

Materials such as, for example, CsI, CsTe, Cs3Sb, diamond and GaN areconsidered for the photocathode 130 or the photocathode sections 131,132. In this case, the photocathode material used is coordinated withthe material of the scintillator 120 in such a way that thescintillation radiation coming from the scintillator 120 can beconverted into free electrons 204 in the photocathode 130 or thesections 130, 131. The photocathode 130, as has already been indicatedabove, can furthermore be embodied in the form of a continuousphotocathode 130 or layer for all channels 165 of the conversion device160, as a result of which simple and cost-effective production ispossible. Particularly in the case of such a configuration, there is thepossibility that the photocathode 130 is arranged on a (separate)carrier element 186 (cf. FIGS. 3, 8 and 14, for example) and can thussimultaneously serve as a channel wall for the channels 165.Alternatively, the possibility of a configuration in the form ofseparate photocathode sections 131, 132 is possible, which can bearranged separately from one another in the channels 165 oncorresponding sections or wall sections. In this respect, a (possible)arrangement on the section 186 and on the layer 180 is indicated in theexemplary embodiments in FIGS. 3 and 5.

For the channel walls 166, 167—shown in the embodiments in FIGS. 3 and5—of the respective channel structures 161, 162 or for the associatedinitial substrate from which the channel structures 161, 162 (or elsedifferently constructed plate-shaped channel structures) and thus thechannel walls 166, 167 thereof can be formed, consideration is given,for example, to a semiconductor material such as silicon, in particular,or else to a glass material. Such materials afford the advantage ofsimple structuring, and enable a high dimensional stability.Furthermore, the possibility is afforded of reliably providing suchmaterials with a wall coating 181 having high secondary electronemission. The wall coating 181 can be formed for example in the contextof a chemical vapor deposition (CVD), which can be carried out inparticular after a structuring of the respective substrate for formingtrenches for the channels 165. It is also possible, if appropriate, toomit such a wall coating 181 or to provide a wall coating 181 only in apartial region. For the channels 165, the length of which can be equalto the height of the scintillator 120, it is possible to provide lateraldimensions in the range of, for example, a few 10 μm to a few 100 μm.

The section 186 shown in FIG. 3 can be a separate carrier elementcomposed of aluminum oxide, for example, which is coated with thephotocathode 130 or photocathode sections 131 and is arranged on thechannel structure 161 (or a differently configured channel structure).Alternatively, the possibility is afforded that the section 186 is not aseparate element, but rather constitutes a (remaining) section of aninitial substrate which was subjected to structuring for the productionof the channels 165 and channel walls 166. In this regard, the section186 can (likewise) comprise a semiconductor material such as silicon, inparticular, or else a glass material.

The layer 180 serving as an entrance window can comprise, for example,silicon oxide (SiOx) or silicon nitride, or else be embodied in the formof a glass window. Such materials can be fully transparent to thescintillation radiation emitted by the scintillator 120. Since suchmaterials can furthermore be suitable for the emission of (secondary)electrons 204, it is possible in this case, contrary to theconfiguration shown in FIG. 3, if appropriate also to provide (partial)omission of the wall coating 181 on the layer 180.

With regard to use as an antireflection layer on the lateral wall 123 ofthe scintillator 120, consideration can furthermore be given toembodying the layer 180 with a thickness which corresponds to onequarter of the wavelength of the scintillation radiation or to amultiple thereof (“quarter-wave layer”). Radiation reflection can be(largely) suppressed as a result. With the use of LSO as scintillatormaterial, in the case of which the scintillation radiation has awavelength of approximately 420 nm, the layer 180 can have a thicknessof 55 nm, for example. Such a layer thickness can be realized reliablyand accurately by the layer 180 being embodied, for example, as a (thin)silicon oxide layer. With the use of LSO as scintillator material havinga refractive index of 1.82 and silicon oxide as material of the layer180 having a refractive index of 1.48, reflection at the lateral wall123 (interface) of less than 1% for example can be achieved in this way.

The layer 180 can furthermore be embodied in the form of a glass windowbonded onto the lateral wall 123 or in the form of a coating of thelateral wall 123 composed of, in particular, silicon oxide or siliconnitride. Alternatively, the possibility is also afforded that the layer180 is produced in the context of production of the channel structures161, 162 (or else of differently constructured plate-shaped channelstructures). By way of example, provision can be made for producing alayer 180 on an initial substrate, wherein channels 165 extending to thelayer 180 are subsequently formed in the substrate by the substratebeing structured, such that the layer 180 constitutes an entrance windowfor the channels 165. Such a structured substrate provided with thelayer 180 can subsequently be arranged on the lateral wall 123 of ascintillator 120 in accordance with the construction shown in FIGS. 3and 5.

Alternatively, the possibility is also afforded of omitting the(optional) layer 180. This affords the possibility of arranging astructured substrate of a channel structure, for example the channelstructures 161, 162 in FIGS. 3 and 5, directly on the lateral wall 123of the scintillator 120. In this regard, furthermore, consideration canbe given to arranging a wall coating 181 or part thereof directly on thelateral wall 123, or else a semitransparent photocathode 130 or aphotocathode section 132 directly on the lateral wall 123 of thescintillator 120.

The electrodes 140, 150 used for accelerating and detecting electrons204 can be embodied in a planar fashion and from an electricallyconductive or metallic material. The detection device 170 or the carriersubstrate 171 thereof can be embodied in particular in the form of asemiconductor or silicon substrate, on which the electrode 150 providedfor trapping electrons 204 is arranged. The detection device 170 canfurthermore also be present in the form of an application specificintegrated circuit (ASIC). In this way, the detection device 170 can bedesigned not only for detecting or reading out a total charge of anelectron avalanche and for generating an output signal on the basisthereof, but also for (at least partly) conditioning or evaluating thesame.

Further possible configurations of detector elements are described withreference to the following figures. In this case, it is pointed outthat, with regard to already described details relating to aspects andcomponents of identical type or corresponding aspects and components,functioning, usable materials, size dimensions, possible advantages,etc., reference is made to the above explanations. In the same way,aspects described below with regard to individual embodiments ofdetector elements can also apply to other embodiments of detectorelements from among those described below.

FIG. 6 shows a schematic perspective illustration of component parts ofa further detector element 102, which comprises a parallelepipedalscintillator 120 and a respective conversion device 160 on each of thefour lateral walls 123 of the scintillator 120. In this case, aconversion device 160 can be constructed in accordance with theapproaches described above. As is furthermore indicated in FIG. 6, thedetector element 102 comprises two electrodes 140, 150 arranged in theregion of the end faces 121, 122 of the scintillator 120 and serving forgenerating an electric field, whereby electrons 204 generated in theconversion devices 160 can be accelerated in the direction of theelectrode 150 and can be trapped by the electrode 150. In this case, theelectrode 150 is a component of a detection device 170 and can bearranged on a carrier substrate 171 thereof. The two electrodes 140, 150are furthermore provided with a frame-shaped structure, in a mannercorresponding to the conversion devices 160 peripherally surrounding thescintillator 120.

The detector element 102 can be designed, in particular, to separatelydetect the electrons 204 generated and multiplied in the differentconversion devices 160. For this purpose, the electrode 150, that isindicated in FIG. 6, has four segments or electrode regions 155 whichare assigned to the individual conversion devices 160 and by means ofwhich electrons 204 “originating” from the individual conversion devices160 can be detected separately from one another. On the basis of this,corresponding output signals can be generated with the aid of thequantities of charge detected by the individual electrode regions 155.

The separate and segment-by-segment detection of electrons 204 generatedby means of different conversion devices 160 affords the possibility ofdetermining, simply and accurately, the lateral location of theinteraction (“x/y position”) of a radiation quantum 200 which excitesthe scintillator 120. In this case, it is possible to make use of thefact that the point in time or the temporal development and/or themagnitude of the charge signals obtained by the electrode regions 155are/is dependent on the proximity of the interaction to the respectivelateral walls 123 on which the conversion devices 160 are arranged. Inorder to determine the lateral interaction location, it is possible, forexample, to form summation and/or difference signals from the individualsignals. Particularly in the case of one possible configuration of thedetection device 170 in the form of an ASIC circuit, this can be carriedout by the detection device 170 itself.

Making it possible to determine a lateral interaction location in ascintillator 120 proves to be expedient for an imaging system in whichthe associated detector is constructed from a plurality of detectorelements 102 constructed in this way. Alongside a high efficiency and ahigh temporal resolution, the relevant detector can have a high lateralspatial resolution as a result even in the case of relatively largelateral scintillator dimensions.

In the embodiments described above, the detection device 170 having thetrapping electrode or anode 150 is arranged in the region of the rearside 121 of the scintillator 120, and the electrode 140 serving ascathode is provided in the region of the front side 122 of thescintillator 120 (see FIGS. 2 and 6). Alternatively, however, aconfiguration symmetrical thereto, with the detection device 170 in theregion of the front side 122 and the electrode 140 in the region of therear side 121, is also possible. In this case, the high-energy radiationto be detected can be transmitted (without interaction) through thedetection device 170 and can be subsequently incident in thescintillator 120, wherein the processes described above can once againoccur.

A further possible variant consists in providing a cathode-anodestructure and detection devices 170 on both end faces 121, 122 of thescintillator 120, and bringing about movements of electrons 204 ofdifferent conversion devices 160 in different or mutually oppositedirections. This affords the possibility of also detecting the height ordepth of an interaction in the scintillator 120.

For exemplary elucidation, FIG. 7 shows a further detector element 103,which comprises a parallelepipedal scintillator 120 and a respectiveconversion device 160 constructed in accordance with the above-describedapproaches on each of the four lateral walls 123 of the scintillator120. The detector element 103 furthermore comprises a mirror-symmetricalelectrode arrangement for bringing about different electron movements.

The electrode arrangement comprises two L-shaped electrodes 141, 152 inthe region of the front side 122, and two further L-shaped electrodes142, 151 in the region of the rear side 121 of the scintillator 120. Ina manner corresponding to the conversion devices 160 peripherallysurrounding the scintillator 120, both the electrodes 141, 152 and theelectrodes 142, 151 in each case form a frame-shaped structure. Theelectrodes 141, 142, 151 and 152 are furthermore arranged on carriersubstrates 171 in the region of the two end faces 121, 122 of thescintillator 120 and can be components of detection devices 170 providedon the two end faces 121, 122.

The electrodes 141, 151 arranged one above the other, as shown in FIG.7, form an electrode pair which can be used to accelerate electrons 204from two of the four conversion devices 160 (on the left and at thefront in the plane of the drawing) adjoining one another or running atright angles with respect to one another in a first direction or in thedirection of the electrode 151. This is indicated in FIG. 7 on the basisof a downwardly directed arrow, which can simultaneously represent thedirection of an electric field that can be generated by the electrodes141, 151. In this case, the electrode 141 serves as cathode, and theother electrode 151 as anode and trapping electrode.

The other two electrodes 142, 152 arranged one above the other also forman electrode pair which can be used to accelerate electrons 204 from theother two conversion devices 160 (on the right and offset toward therear in relation to the plane of the drawing) in a second direction,opposite thereto, in the direction of the electrode 152.

This is indicated in FIG. 7 on the basis of an upwardly directed arrow,which can simultaneously represent the direction of an electric fieldthat can be generated by the electrodes 142, 152. In this case, theelectrode 142 functions as cathode, and the other electrode 152 as anodeand trapping electrode.

The acceleration and detection of electrons 204 or electron avalanchesin different directions affords the possibility of determining theheight or depth (“z-position”) of an interaction of a radiation quantum200 that excites the scintillator 120. In this case, it is possible tomake use of the fact that the point in time or the temporal developmentand/or the magnitude of the quantities of charge detected via thetrapping electrodes 151, 152 are/is dependent on the proximity of theinteraction to the front or rear side 122, 121 of the scintillator 120.In this case, too, it is possible to form corresponding summation and/ordifference signals from individual measurement signals obtained by meansof the two trapping electrodes 151, 152 or detection devices 170.

In the case of the detector element 103 from FIG. 7, provision canalternatively be made, contrary to the illustration in FIG. 7, for usingthe electrode pair 141, 151 to produce an electron movement directedupward in the direction of the electrode 141 or front side 122 of thescintillator 120, and using the electrode pair 142, 152 to produce anelectron movement directed downward in the direction of the electrode142 or rear side 121 of the scintillator 120, which can be defineddepending on the voltage respectively applied to the electrode pairs141, 151 and 142, 152. In the case of such “mirror-symmetrical”functioning, the above-indicated functions of the electrodes 141, 142,151 and 152 as cathode and (trapping) anode are also interchanged. Inthis regard, provision can furthermore be made for designing thedetector element 103 for a flexible mode of operation in which allelectrodes 141, 142, 151, 152 can be operated optionally as cathode oranode. In this case, it is also possible to “drive” the electrodes 141,142, 151, 152 in such a way that the electrode pairs 141, 151 and 142,152 bring about electron movements in each case in the same direction.

Instead of designing a detector element with only a single scintillator120, modular configurations of detector elements comprising a pluralityof scintillators 120 arranged alongside one another are also possible,which can be constructed in accordance with the approaches demonstratedabove. In this case, conversion devices 160 assigned to the individualscintillators 120 and serving for converting scintillation radiationinto (multiplied) electrons 204 can be arranged in interspaces betweenthe scintillators 120 and on opposite lateral walls 123 of thescintillators 120. One possible exemplary embodiment will be describedin greater detail with reference to the following figures.

FIG. 8 shows a schematic plan view illustration of two(parallelepipedal) scintillators 120 arranged alongside one another andconversion devices 160 assigned to the scintillators 120, saidconversion devices being arranged in an interspace between thescintillators 120 on opposite lateral walls 123 of the scintillators120. The conversion devices 160 have the plate-shaped construction withthe channel structure 161 as described with reference to FIG. 3. In thiscase, web-shaped channel walls 166 of the channels 165 are connected atone end to the lateral wall 123 of the associated scintillator 120 or tothe layer 180 (entrance window) optionally provided on the lateral wall123.

At an opposite end of the channel walls 166 with respect thereto, acarrier element 186 provided with a reflectively operating photocathode130 on both sides is provided, said carrier element being assigned tothe two conversion devices 160 or channel structures 161. By means ofthe coated carrier element 186, the channels 165 of the two channelstructures 161 are closed at this location, and each channel 165 of thetwo channel structures 161 is provided with an associated photocathodesection 131. On account of the joint utilization of the carrier element186 coated with the photocathodes 130 on both sides for both conversiondevices 160, a simple and cost-effective detector construction is madepossible.

FIG. 9 shows a schematic perspective illustration of a detector element104 which is constructed in a manner corresponding to FIG. 8 andcomprises two scintillators 120 arranged alongside one another andassociated conversion devices 160, including the carrier element 186provided with photocathodes 130, in the interspace between thescintillators 120. The detector element 104 furthermore comprises thecomponents described above, i.e. electrodes 140, 150 at the ends of thechannels 165 for accelerating and trapping electrons 204, and a carriersubstrate 171 or a detection device 170, which are assigned to thescintillators 120. In this case, the two scintillators 120 can be placedor supported on the carrier substrate 171. The electrode 150 can bedesigned for joint, or alternatively separate or segment-by-segment,trapping of electrons 204 of the individual conversion devices 160. Forthis purpose, the electrode 150 can comprise electrode regions assignedto the individual conversion devices 160 in a manner comparable with theexemplary embodiment shown in FIG. 6, or else can be subdivided intoseparate electrodes (not illustrated).

FIG. 9 furthermore indicates a presence of a housing 190 arranged on thecarrier substrate 171, said housing surrounding the scintillators 120.The housing 190 can be utilized for providing a (global) vacuum or anevacuated environment for all channels 165 of the conversion devices160. The housing 190 can furthermore be used for carrying the electrode140.

In accordance with the approaches described above, in the case of thedetector element 104 as well, conversion devices 160 can be arranged onall four lateral walls 123 of the scintillators 120. In this case,associated electrodes 140, 150 can be designed for accelerating andtrapping electrons 204 of the two scintillators 120 and, in a mannercomparable with FIG. 6, comprise a respective frame-shaped section perscintillator 120. Here, too, the electrode 150 can comprise, ifappropriate, electrode regions assigned to the individual conversiondevices 160, or else can be subdivided into separate electrodes in orderto be able to detect, in particular, a lateral interaction location inthe scintillators 120. A configuration comparable with FIG. 7 is alsopossible, that is to say that provision is made of one (per scintillator120) frame-shaped cathode-anode structure and detection devices 170 onboth end faces 121, 122 of the scintillators 120, as a result of whichelectrons 204 of different conversion devices 160 of a scintillator 120can be accelerated in different directions, and by detecting the same itis possible to determine an “interaction depth” in the scintillators120.

These approaches correspondingly also hold true for such configurationsof the detector element 104 in which the detector element 104 comprisesmore than the two scintillators 120 arranged alongside one another asshown. In this case, the scintillators 120 can be arranged for examplein a pixel- or matrix-type fashion in the form of rows and columnsalongside one another, and on the carrier substrate 171, and can onceagain be surrounded by a corresponding housing 190. In such aconfiguration, too, conversion devices 160 can be arranged on all fourlateral walls 123 of the scintillators 120, wherein conversion devices160 can be present (in each case) in an interspace between twoscintillators 120 in accordance with the construction illustrated withreference to FIGS. 8 and 9.

A plate-shaped conversion device 160, for example having the channelstructure 161 shown in FIG. 3, can be realized in a space-saving, simpleand cost-effective manner on a lateral wall 123 of a scintillator 120.This applies, in particular, to the configuration shown in FIG. 8, inwhich the carrier element 186 coated with photocathodes 130 on bothsides is utilized for two conversion devices 160.

For exemplary elucidation, FIGS. 10 to 13 illustrate a schematic planview illustration of steps for producing the construction shown in FIG.8. In accordance with FIG. 10, a planar initial substrate 168, forexample a thin silicon substrate, is provided for each of the conversiondevices 160, channels 165 (or trenches as “precursors” of the laterchannels 165) being produced in said substrate. They are separated fromone another by channel walls 166. By way of example, a dry etchingprocess can be carried out for this purpose. The trenches or channels165 extend perpendicular to the plane of the drawing in FIGS. 10 to 13and furthermore, at a “top side and underside” running parallel to theplane of the drawing, adjoin corresponding plate-shaped sections of thesubstrate 168 by which the channel walls 166 are connected.

As is furthermore shown in FIG. 11, a carrier element 186 is provided,which can be, for example, a substrate or a plate composed of aluminumoxide. A photocathode material for a respective photocathode 130 isdeposited on both sides of the carrier element 186. In this case, by wayof example, GaN can be deposited by means of a CVD method.

Furthermore, the scintillators 120 are provided with a layer 180 servingas an entrance window on the lateral walls 123, as is indicated in FIG.12 on the basis of a scintillator 120 and the coating of two lateralwalls 123 of the scintillator 120. By way of example, LSO is consideredas scintillator material. The layer 180 is, for example, a silicon oxidelayer having a layer thickness of 55 nm, which can be realized by meansof a suitable coating method.

Subsequently, as is indicated in FIG. 13, two scintillators 120 coatedin this way, and therebetween two structured substrates 168 and thecarrier 186 provided with the photocathodes 130 are positioned withrespect to one another in the arrangement illustrated in FIG. 13, andare connected to one another or “clamped together”. In this way, theconversion devices 160 provided on the lateral walls 123 of thescintillators 120, or the channel structures 161 of said conversiondevices, are substantially completed.

Afterward, the abovementioned “top side and underside” sections of thesubstrates 168 which run parallel to the plane of the drawing in FIGS.10 to 13 and via which the channel walls 166 are connected can beremoved, such that the opposite ends of the channels 165 are exposed.This can be done by means of chemical mechanical polishing (CMP), forexample. Furthermore, electrodes 140, 150 (or corresponding electrodesections) can be provided in these regions and thus at the ends of thechannels 165, and this construction can be arranged on a correspondingcarrier substrate 171, such that a structure corresponding to FIG. 9 canbe present.

With regard to a configuration comprising a plurality of scintillators120 arranged, in particular, in a matrix-type fashion with respect toone another, the abovementioned steps can be carried out in an analogousmanner. In this case, two scintillators 120 adjoining one another can ineach case be connected in the manner illustrated with reference to FIG.13. For scintillators 120 arranged at the edge of the matrix,consideration can furthermore be given to leaving the associated outerlateral walls 123 uncoated, or to arranging thereon structuredsubstrates 168 and carrier elements 186 coated with a photocathode 130only on one side.

A modular configuration of a detector element comprising a plurality ofscintillators 120 arranged alongside one another can also be realizedwith conversion devices 160 in which a differently constructed channelstructure deviating from the channel structure 161 from FIG. 3 is used.In particular, the channel structure 162 having the semitransparentphotocathode 130 shown in FIG. 5 can also be used. In this case, thepossibility is likewise afforded that two channel structures 162 of thistype, in the manner similar to the construction shown in FIG. 8, arearranged in each case in an interspace between two scintillators 120 onthe opposite lateral walls 123 thereof.

In the case of such a configuration, consideration can furthermore begiven to “combining” two channel structures 162 provided in aninterspace to form a common channel structure on both sides. By way ofexample, the channel wall 167 shown in FIG. 5 can function as a centralweb, on the opposite sides of which the construction having the channels165 as shown in FIG. 5 is provided “mirror-symmetrically”, such thatchannel walls 166 extending “laterally” from the channel wall 167,contrary to the “one-sided” construction from FIG. 5, can be provided onboth opposite sides of the channel wall 167. In this case, there islikewise the possibility that the arrangement comprising the channelwall 167 and the channel walls 166 extending on both sides thereof isproduced by trenches being produced in a substrate, with the removal ofsubstrate regions between the channel walls 166, 167.

Furthermore, with the use of the channel structure 162 or elsedifferently constructed channel structures, the above-describedconfigurations are likewise possible in which, for example, provision ismade of conversion devices 160 on all lateral walls 123 of ascintillator 120, a matrix arrangement comprising a plurality ofscintillators 120, and/or an electrode structure comprising electrodes140, 150 having frame-shaped sections per scintillator 120. Furthermore,consideration is given to separate or segment-by-segment detection ofelectrons 204 of different conversion devices 160 in accordance with theapproach shown in FIG. 6, and to bringing about different electronmovements in accordance with the approach shown in FIG. 7.

Such embodiments can be realized with correspondingly configuredelectrode arrangements (separate electrode regions, electrode pairs fordifferent conversion devices). For further details in this respect,reference is made to the above explanations.

As has already been indicated above, the detector concept describedhere, that of providing a conversion device 160 on a (at least one)lateral wall 123 of a scintillator 120, is not restricted toplate-shaped conversion devices 160 having a channel structurecomprising a structured substrate (for example the channel structure 161or 162).

In one alternative configuration, a conversion device 160 can comprise achannel structure 163 in which the channels 165 are formed by cutouts ordepressions 125 formed in the lateral wall 123 of a scintillator 120,and, consequently, the scintillator 120 has a lateral wall 123 having astructured surface. This enables a particularly space-saving, simple andcost-effective construction, which is advantageous in particular formodular configurations comprising a plurality of scintillators 120. Onepossible embodiment will be described in greater detail with referenceto the following figures.

FIG. 14 shows a schematic plan view illustration of two scintillators120 arranged alongside one another and comprising conversion devices 160or channel structures 163 constructed in accordance with this approachon the lateral walls 123. A perspective illustration, with the aid ofwhich the (substantially) parallelepipedal construction of thescintillators 120 once again becomes clear, is furthermore shown in FIG.15.

In this case, the mutually opposite lateral walls 123 of thescintillators 120 have depressions 125 through which channels 165 areformed. The depressions 125 and thus the channels 165, which runparallel to a longitudinal axis of the respective scintillator 120, saidlongitudinal axis extending between the end faces 121, 122, can have anelliptic or oval geometry in plan view. Alternatively, other shapes forthe depressions 125 and thus the channels 165, such as a rectangular ortriangular shape, for example, are also possible (not illustrated).

Furthermore, the carrier element 186 provided with reflectivelyoperating photocathodes 130 on both sides, as described above withreference to FIGS. 3 and 8, is arranged in an interspace between thescintillators 120. The depressions 125 and thus channels 165 of theconversion devices 160 on the lateral walls 123 of the associatedscintillators 120 are closed in this way. Furthermore, the channels 165are thereby assigned corresponding sections of the photocathode 130which can be used to convert scintillation photons 202 that are emittedin the direction of the respective lateral wall 123 of a scintillator120 and enter into the channels 165 into photoelectrons 204 in themanner described above.

As is furthermore shown in FIG. 14, the depressions 125 of thescintillators 120 are furthermore preferably provided with a wallcoating 181, for example composed of silicon oxide. As in the case ofthe exemplary embodiments described with reference to FIGS. 3 and 5,said coating serves to make it possible to liberate a multiplicity ofelectrons 204 per impact process of an electron 204 with the channelwall. For this purpose, the wall coating 181 comprises, in particular, amaterial having high secondary electron emission.

FIG. 14 furthermore illustrates the process of generation andmultiplication of electrons 204 that takes place in a channel 165 of thechannel structure 163. The scintillation photons 202 emitted by thescintillator 120 in the direction of the lateral wall 123 can penetratethrough the (semitransparent) wall coating 181 and enter into theinterior of the channel 165, pass further to the reflective photocathode130 and be absorbed by the latter. On the basis of this, thephotocathode 130 can emit electrons 204 into the interior of the channel165, wherein electrons 204 are liberated as a result of impacts with thewall coating 181, which electrons for their part can likewise contributeto the electron multiplication within the channel 165 as a result ofimpacts with the wall coating 181. In this case, provision is made foraccelerating the electrons 204 once again along the channels 165,wherein corresponding electrodes 140, 150 can be provided at the ends ofthe channels 165.

For elucidation, FIG. 16 illustrates a detector element 105 constructedin a manner corresponding to FIGS. 14 and 15. The detector element 105once again comprises the components described above, i.e. electrodes140, 150 for accelerating and trapping electrons 204, and a carriersubstrate 171 or a detection device 170. In this case, the twoscintillators 120 can be placed or supported on the carrier substrate171. The electrode 150 can be designed for joint, or alternativelyseparate or segment-by-segment, trapping of electrons 204 of theindividual conversion devices 160. For this purpose, the electrode 150can comprise electrode regions assigned to the individual conversiondevices 160 in a manner comparable with the exemplary embodiment shownin FIG. 6, or else can be subdivided into separate electrodes (notillustrated).

FIG. 16 furthermore indicates a presence of a housing 190 arranged onthe carrier substrate 171, which housing 190 can be utilized forproviding a (global) vacuum for all channels 165 of the conversiondevices 160. The housing 190 can furthermore be used for carrying theelectrode 140.

In accordance with the approaches described above, in the case of thedetector element 105 as well, conversion devices 160 having channelstructures 163 can be arranged on all four lateral walls 123 of thescintillators 120. In this case, associated electrodes 140, 150 can bedesigned for accelerating and trapping electrons 204 of the twoscintillators 120 and, in a manner comparable with FIG. 6, comprise arespective frame-shaped section per scintillator 120. Here, too, theelectrode 150 can comprise, if appropriate, electrode regions assignedto the individual conversion devices 160, or else can be subdivided intoseparate electrodes in order to be able to detect, in particular, alateral interaction location in the scintillators 120. A configurationcomparable with FIG. 7 is also possible, that is to say that provisionis made of one (per scintillator 120 frame-shaped) cathode-anodestructure and detection devices 170 on both end faces 121, 122 of thescintillators 120, as a result of which electrons 204 of differentconversion devices 160 of a scintillator 120 can be accelerated indifferent directions, and by detecting the same it is possible todetermine an “interaction depth” in the scintillators 120.

These approaches correspondingly also hold true for configurationscomprising only one scintillator 120, or comprising more than twoscintillators 120, which can be arranged, in particular, in amatrix-type fashion on the carrier substrate 171. In this case, too,conversion devices 160 having channel structures 163 can be arranged onall four lateral walls 123 of the scintillators 120, wherein conversiondevices 160 can be present (in each case) in an interspace between twoscintillators 120 in accordance with the construction elucidated withreference to FIG. 14. In a configuration comprising only onescintillator 120, which has a conversion device 160 or channel structure163 on a (at least one) lateral wall 123, or for the case of an outerlateral wall 123 of a scintillator 120 of a scintillator arrangement orscintillator matrix, provision can be made for the depressions 125 orchannels 165 formed at the respective lateral wall 123 to be closed witha carrier element 186 coated with the photocathode 130 only on one side.

Modifications are also conceivable for the conversion device 160 havingthe channel structure 163 as shown in FIG. 14. For example, provisioncan be made for providing the depressions 125 or a partial regionthereof with semitransparent photocathodes or photocathode sections,such that functioning comparable to the channel structure 162 from FIG.5 can be present. In the case of such a configuration as well,consideration can be given to closing the depressions 125 or channels165 at the lateral wall 123 with a corresponding substrate or carrierelement 186. In this case, a wall coating 181 used for electronmultiplication can be arranged in a manner adjoining a photocathodesection of a depression 125, and also on the carrier element 186provided for closure. With regard to shared utilization of such acarrier element 186 for conversion devices 160 having channel structures163 on mutually opposite lateral walls 123 of two scintillators 120, thecarrier element 186 can be provided with a wall coating 181 on bothsides.

A conversion device 160 having one of the above-described channelstructures 161, 162, 163 (and possibly modifications thereof) can beembodied in a relatively space-saving manner and with a relatively smallwidth or thickness on account of the channels 165 arranged alongside oneanother in a plane at a lateral wall 123 of a scintillator 120. Thisaffords the possibility, in the case of modular configurationscomprising a plurality of scintillators 120 arranged alongside oneanother, as illustrated in FIGS. 9 and 16, of also keeping theinterspace between two scintillators 120 relatively small. By way ofexample, the interspace or distance between two scintillators 120 can beless than 100 μm. In this way, a detector element comprising a pluralityof scintillators 120 (in particular arranged in a matrix-type fashion)can have a very high filling factor (ratio of active area, i.e. all“sensitive” front sides 122, of the scintillators 120 to irradiatedtotal area), which can be greater than 98%.

The detector elements described above are designed to convert thescintillation radiation emitted to a (at least one) lateral wall 123 ofa scintillator 120 into multiplied electrons 204 by means of aconversion device 160 and to detect the electrons 204. However, an“extension” of the detector elements is also possible to the effect thatin addition part of the radiation emitted to one or both end faces 121,122 of a scintillator 120 is also converted into electrons 204 that aredetected. If appropriate, a relatively high efficiency can be obtainedas a result.

For exemplary elucidation, FIG. 17 shows a schematic lateralillustration of a further detector element 106, which is designed forsuch functioning. The detector element 106 comprises a parallelepipedalscintillator 120, on the lateral wall 123 of which a conversion device160 embodied in accordance with the approaches demonstrated above isarranged. An electric field can be generated by means of electrodes 140,150, whereby electrons 204 converted and multiplied in the conversiondevice 160 can be accelerated to the electrode 150 and trapped by thelatter. The electrode 150, as indicated in FIG. 17, is part of adetection device 170 provided for detecting electrons 204, whichdetection device can additionally comprise a substrate 171, on which theelectrode 150 is arranged.

Furthermore, an additional semitransparent photocathode section 139 isarranged at the rear side 121 of the scintillator 120, with the aid ofwhich photocathode section scintillation photons 202 emerging at thislocation can be converted into electrons 204. Furthermore, amicrochannel plate 169 is arranged below the photocathode 139, in whichmicrochannel plate the electrons 204 coming from the photocathode 139can be multiplied further, and can subsequently be detected by theelectrode 150 arranged below the microchannel plate 169. As is shown inFIG. 17, the electrode 150 can be designed for separately detecting theelectrons 204 coming from the conversion device 160 and from themicrochannel plate 169, and for this purpose can have electrode regions158, 159 assigned to the microchannel plate 169 and to the conversiondevice 160.

The microchannel plate 169 is provided with a multiplicity of channelswithin which the electrons 204, as in the channels 165 of the conversiondevice 160, can be multiplied in an avalanche-like manner as a result ofimpact processes with the channel walls. During operation, an electricalvoltage (acceleration voltage) is applied between the main surfaces ormain sides, i.e. between front and rear sides of the microchannel plate169, between which the channels thereof also extend, as a result ofwhich an electric field is present along the channels. This can beeffected with the aid of the electrode 150 at the rear side of themicrochannel plate 169, and with the aid of an additional electrode ordynode (not illustrated) at the front side of the microchannel plate169.

The concept illustrated in FIG. 17 of (also) converting thescintillation radiation emerging at an end face of a scintillator 120into electrons 204 and multiplying the latter, can be provided in all ofthe above-described configurations of detector elements (for examplecomprising conversion devices 160 on all four lateral walls 123, modularconfigurations comprising a plurality of scintillators 120, etc.).Furthermore, it is possible also to detect the scintillation radiationemitted at both end faces 121, 122 of a scintillator 120, wherein theconstruction comprising a microchannel plate 169 and a detection device170 as shown in FIG. 17 can be provided on both end faces 121, 122.

The embodiments explained with reference to the figures constitutepreferred or exemplary embodiments of the invention. Alongside theembodiments described and depicted, further embodiments are conceivablewhich can comprise further modifications and/or combinations of featuresdescribed. Moreover, the detectors or detector elements explained withreference to the figures can also comprise further structures (notillustrated) alongside the structures shown and described. Furthermore,it is possible to use different materials than those indicated above fora detector element or the components thereof, and to design a detectorelement or the components thereof with different dimensions than thoseindicated.

In the same way, a detector element or the components thereof can beembodied with other geometries which deviate from the exemplaryembodiments shown in the figures. Other geometries can be considered forexample for electrodes for accelerating and trapping electrons, and forelectrode arrangements for bringing about electron movements in oppositedirections. Moreover, a conversion device 160 embodied as a“two-dimensional channel system” and having channels 165 running alongor arranged in a plane on a lateral wall of a scintillator 120 can havedifferent shapes than those described above.

This is the case, in particular, if a scintillator 120 has, instead of aparallelepipedal shape, a different shape having two mutually oppositeend faces and a (at least one) lateral wall between the end faces,wherein the end faces are connected to one another via the lateral wall.One possible example is a scintillator 120 having a cylindrical orcircular-cylindrical shape. In this case, a conversion device 160arranged on the lateral wall (lateral surface) of such a scintillator120 can comprise channels 165 arranged in a curved plane or area in amanner corresponding to the shape of the lateral wall of thescintillator 120. In this case, by way of example, a configurationcomprising a grooved channel structure 163 corresponding to FIG. 14 canbe provided, wherein the lateral wall of the scintillator 123 comprisesa structured surface, and the channels 165 are present in the form ofindentations or depressions formed in the lateral wall of thescintillator 120. In this configuration, a curved or circular carrierelement 186 can be used for closing the channels 165. Said carrierelement can furthermore be provided with a photocathode 130 on the sidefacing the channels 165. Electrodes 140, 150 used for accelerating andtrapping electrons can in this case be embodied in a curved or circularfashion. In this case, provision can furthermore be made for arrangingthe channels 165 along the entire periphery of the scintillator 120 inorder to convert scintillation radiation emitted to the lateral wallinto electrons in an efficient manner.

With regard to a scintillator 120 having two mutually opposite end facesand a plurality of lateral walls situated therebetween, provision canfurthermore be made for arranging a conversion device 160 only on oneindividual lateral wall or conversion devices 160 only on a portion ofthe lateral walls, such that one or more lateral walls are utilized notjust for converting scintillation radiation into multiplied electrons.It is also possible, in the case of a scintillator 120 having one or aplurality of lateral walls arranged between two end faces, for one or aplurality of lateral walls to be provided with a conversion device 160only in a partial region, rather than completely.

With regard to an electrode 150, 151, 152 used for trapping multipliedelectrons, it can furthermore be provided that, instead of a planarconfiguration having one or, if appropriate, a plurality of electroderegions, such an electrode is embodied in the form of separateindividual electrodes which are assigned in each case to an individualor a plurality of channels 165 of a conversion device 160.

Furthermore, the possibility is afforded of separately detectingelectrons of different subsections of an individual or one and the sameconversion device 160. In this case, in particular, an electrode 150subdivided into different electrode regions can be used. Such aconfiguration is possible for example for the above-described exemplaryembodiment with a circular-cylindrical scintillator 120 and a (in planview) curved or circular conversion device 160 arranged on the lateralwall. In this case, an annular trapping electrode 150 can be provided,which is subdivided into four electrode regions, for example, in orderto separately detect electrons generated and multiplied by four sections(arranged alongside one another) of the conversion device 160. On thebasis of this or by evaluating the different charge signals obtained viathe electrode regions (“summation and/or difference formation”), it ispossible to determine a lateral interaction location in thecircular-cylindrical scintillator 120.

In the same way it is conceivable for electrons of different subsectionsof an individual conversion device 160 to be accelerated in different oropposite directions, and detected separately, which is possible with theaid of a corresponding electrode arrangement arranged on the conversiondevice 160. For the above-described exemplary embodiment with acircular-cylindrical scintillator 120 and a (in plan view) curved orcircular conversion device 160 arranged on the lateral wall, by way ofexample, corresponding annular cathode-anode structures and detectiondevices 170 can be provided on both end faces of the scintillator 120and can be used to deflect electrons of a (for example semi-annular)section of the conversion device 160 in one direction and electrons ofanother (semi-annular) section in a direction opposite thereto. On thebasis of this or by evaluating charge signals (“summation and/ordifference formation”) which can be obtained with the aid of the(trapping) anodes arranged on the different end faces, it is possible todetermine an “interaction depth” in the circular-cylindricalscintillator 120.

With regard to the approach demonstrated above in particular withreference to FIGS. 8 and 14, that of jointly utilizing componentsarranged in an interspace between two scintillators 120 for twoconversion devices 160, other configurations are also possible. By wayof example, the carrier element 186 shown in FIG. 8, like the channelwalls 166, can be formed from a shared initial substrate and thus serveas a central web of the channel walls 166 extending “laterally”therefrom. In this configuration, it can furthermore be provided that,instead of the continuous photocathodes 130, separate photocathodesections of the channels 165 are arranged on both sides at the “centralweb” 186, corresponding to the construction comprising the photocathodesections 131 as illustrated in FIG. 3.

Although the invention has been described and illustrated morespecifically in detail by means of preferred exemplary embodiments, theinvention is nevertheless not restricted by the examples disclosed andother variations can be derived therefrom by a person skilled in theart, without departing from the scope of protection of the invention.

1. A radiation detector (100; 101; 102; 103; 104; 105; 106), comprising:a scintillator (120) for generating electromagnetic radiation (202) inresponse to the action of incident radiation (200), wherein thescintillator (120) has two mutually opposite end faces (121; 122) and alateral wall (123) between the end faces (121; 122); a conversion device(160) arranged on the lateral wall (123) of the scintillator (120) andhaving a plurality of channels (165), wherein each channel (165) has aphotocathode section (130; 131; 132) for generating electrons (204) inresponse to the action of the electromagnetic radiation (202) generatedby the scintillator (120), which electrons are multipliable by impactprocesses in the channels (165), and wherein the plurality of channelsof the conversion device run parallel to a longitudinal axis of thescintillator, the longitudinal axis extending between the end faces; anda detection device (170) for detecting electrons (204) multiplied in thechannels (165) of the conversion device (160).
 2. The radiation detectoras claimed in claim 1, wherein the detection device (170) has anelectrode (150; 151; 152) for trapping electrons (204), said electrodebeing arranged at one end of the channels (165), and wherein theradiation detector has a counterelectrode (140; 141; 142) for bringingabout a movement of electrons (204) to the electrode (150; 151; 152) ofthe detection device (170), said counterelectrode being arranged at anopposite end of the channels (165).
 3. The radiation detector as claimedin claim 1, wherein the lateral wall (123) of the scintillator (120) isembodied in a planar fashion, and wherein the conversion device (160) isembodied in the form of a plate-shaped structure on the lateral wall(123) of the scintillator (120).
 4. The radiation detector as claimed inclaim 1, wherein the lateral wall (123) of the scintillator (120) hasdepressions (125) through which the channels (165) of the conversiondevice (160) are formed.
 5. The radiation detector as claimed in claim1, wherein the photocathode sections (131; 132) of the channels (165) ofthe conversion device (160) are embodied in the form of a continuousphotocathode (130).
 6. The radiation detector as claimed in claim 5,wherein the photocathode (130) is arranged on a carrier element (186).7. The radiation detector as claimed in claim 1, wherein the lateralwall (123) of the scintillator (120) is provided with a layer (180) thatis transmissive to the electromagnetic radiation (202) generated by thescintillator (120).
 8. The radiation detector as claimed in claim 1,wherein the channels (165) of the conversion device (160) have a wallcoating (181) designed to liberate a plurality of electrons (204) perimpact process of an electron (204).
 9. The radiation detector asclaimed in claim 1, wherein the plurality of channels (165) of theconversion device are arranged in a plane alongside one another on thelateral wall of the scintillator.
 10. The radiation detector as claimedin claim 1, wherein the scintillator (120) is embodied in aparallelepipedal fashion and has four lateral walls (123) between theend faces (121; 122), and wherein a conversion device (160) having aplurality of channels (165) is arranged on each of the four lateralwalls (123).
 11. The radiation detector as claimed in claim 1, whereinthe detection device (170) is designed for separately detectingelectrons (204) generated in channels (165) of different conversiondevices (160) or in channels (165) of different subsections of aconversion device (160).
 12. The radiation detector as claimed in claim1, wherein the radiation detector is designed to bring about a movementof electrons (204) in channels (165) of different conversion devices(160) or in channels (165) of different subsections of a conversiondevice (160) in different directions.
 13. The radiation detector asclaimed in claim 1, wherein the radiation detector is additionallydesigned to convert part of the electromagnetic radiation (202)generated in the scintillator (120) and emerging at an end face (121;122) into electrons (204) and to detect the electrons (204).
 14. Theradiation detector as claimed in claim 1, comprising: two scintillators(120) arranged alongside one another; conversion devices (160) arrangedin an interspace between the scintillators (120) and on opposite lateralwalls (123) of the scintillators (120) and assigned to the scintillators(120) and having a plurality of channels (165); and a detection device(170) for detecting electrons (204), said detection device beingassigned to the conversion devices (160).
 15. An imaging systemcomprising: a radiation detector comprising: a scintillator forgenerating electromagnetic radiation in response to the action ofincident radiation, wherein the scintillator has two mutually oppositeend faces and a lateral wall between the end faces; a conversion devicearranged on the lateral wall of the scintillator and having a pluralityof channels, wherein each channel has a photocathode section forgenerating electrons in response to the action of the electromagneticradiation generated by the scintillator, which electrons aremultipliable by impact processes in the channels, and wherein theplurality of channels of the conversion device run parallel to alongitudinal axis of the scintillator, the longitudinal axis extendingbetween the end faces; and a detection device for detecting electronsmultiplied in the channels of the conversion device.